Cellular protein damage is combated in bacteria, nematodes, flies, plants, and mammals, including humans, by protein repair reactions. Protein L-isoaspartate (D-aspartate) O-methyltransferase (PIMT) catalyzes the repair of protein damage via a methylesterification reaction, which initiates the conversion of L-isoaspartyl residues back to normal L- aspartyl residues. PIMT is thought to help fight age- and oxidation-induced protein damage, yet our understanding of this highly conserved enzyme is incomplete. To further examine its significance, this study will investigate the role PIMT activity plays in certain plants at the molecular level and its impact on the organism as a whole. Using a biochemical approach, the activity of recombinant Arabidopsis thaliana PIMT will be characterized after affinity-tag purifying it from overexpressing Escherichia coli cells. In addition, the biological impact on Arabidopsis when one or both of its PIMT genes are disrupted will be analyzed in commercially available T-DNA insertion mutant plants and strains bred from these. Since light induced oxidation reactions may regulate the expression of PIMT in Zea mays (corn), the endogenous PIMT activity will be measured in homogenates from corn plants grown under high light conditions. To understand PIMT activity in tropical plants, which face an expected increase in spontaneous damage generated by high temperature and light conditions, the endogenous PIMT activity in Musa acuminata (banana) will be characterized by similar techniques. Overall, a better understanding of PIMT enzyme may lead to treatments for protein damage in humans and perhaps the partial reversal of human aging phenotypes.